The present invention relates to an industrial truck having an electric travel drive that can be switched by controls to regenerative operation in order to brake the industrial truck. In regenerative operation, the travel drive is used as a generator, the generated current of which is supplied to a battery.
An automated spring-operated brake for an industrial truck is known from EP 2 006 563 A1, the entire contents of which is incorporated herein by reference. A magnet arrangement in the form of an eddy current brake that interacts with a brake provided with friction linings can be provided in the known industrial truck.
An industrial truck is known from DE 10 2006 051 264 A1, the entire contents of which is incorporated herein by reference, with a drive axle that is equipped with an electrical or hydraulic traction motor for the travel drive, and that is equipped with an eddy current brake. To exploit the advantages of an eddy current brake, the industrial truck is equipped with an internal combustion engine. The provided electric motor is exclusively operated as a motor and not as a generator.
An industrial truck with a brake device is known from DE 10 2006 051 264 A1, the entire contents of which is incorporated herein by reference, that has an electric or hydraulic traction motor for the travel drive and at least one brake device for braking a traveling motion of the forklift, and the brake device is designed as an eddy current brake. When an electric traction motor is used, it is exclusively operated as a motor and not as a generator.
A brake system for a vehicle with an electric motor is known from DE 10 2006 019 494 A1, the entire contents of which is incorporated herein by reference, that has a mechanical brake as well as additionally an electric brake. Depending on the actuation of a brake actuation device, first only the electric brake is activated which is followed by the mechanical brake.
A control and/or regulating device for a retarder as an additional brake device, especially for vehicles, is known from DE 197 31 847 A1, the entire contents of which is incorporated herein by reference. The control and regulation device has a controllable power semiconductor as an actuator for the current flowing through the retarder which can be adjusted depending on one or more operating parameters of the vehicle. A special feature of the control and regulating device is that it is automatically shut off at a speed below a threshold.
A control algorithm for an eddy current brake system is known from DE 103 10 105 A1, the entire contents of which is incorporated herein by reference, by means of which a control current is determined as a function of the feedback current depending on a determined feedback current of a retarder assembly and a rotor speed of the retarder assembly.
An additional braking device for trucks and omnibuses with an electric eddy current brake is known from DE 39 08 234 A1, the entire contents of which is incorporated herein by reference, where the eddy current brake is equipped with its own electric generator, the excitation current of which is drawn from the vehicle onboard power supply to achieve a minimum load on the onboard power supply while the eddy current brake is operating.
A control algorithm for an eddy current brake in a motor vehicle is known from GB 2 387 418 A, the entire contents of which is incorporated herein by reference. To regulate the eddy current brake, a feedback current from the eddy current brake and a rotor speed of the rotor of the eddy current brake are determined, and the control current for the eddy current brake is determined by a regulator from a setpoint value for the eddy current brake.
The control of a vehicle is known from US 2010/0039054 A1, the entire contents of which is incorporated herein by reference, in which electrical power is provided for an electric travel drive with the assistance of a mechanically operated generator. When an eddy current brake is used and the electrical power generated thereby is greater than the power required for the travel drive, the electric travel drive is supplied from the eddy current brake.
An automatic spring operated brake for an industrial truck is known from EP 2 006 563 A1, the entire contents of which is incorporated herein by reference, that has an electromagnetically actuatable parking brake.
An electric travel drive for a vehicle is known from WO 2007/053889 A1, the entire contents of which is incorporated herein by reference, where a brake disc is also designed as a rotor for an electric motor.
To brake industrial trucks, it is often unsuitable to use a single stage friction brake since, being designed for a maximum load, it excessively brakes a vehicle without a load.
The use of the travel motor as a generator is known for electrically operated industrial trucks such as, for example, reach trucks, high lift trucks and low lift trucks, etc. In the design of the travel drive, the demand is shifted to motor operation with the aim of minimizing the output of the travel drive for reasons of economy and energy efficiency. Consequently, however, in particular at high speeds and high payloads, the output of the travel drive in generator operation is frequently insufficient to achieve the required stopping distances.